The requirements for fast acting interconnecting joints in manufacturing, robotics, teleoperation equipment, etc., with several degrees of freedom (DOF) have been at least partially satisfied using a variety of different methods. In many cases six degrees of freedom must be imparted to an object, however, the performance available with existing systems having this number of degrees of freedom is limited in some ways.
Generally in sensitive systems the operator controls the position or velocity of the slave device by moving the teleoperated master or joystick and the joystick exerts forces on the operators hand that are proportional to those exerted by the slave.
There has been significant work done in developing such devices. However, serial kinematic mechanisms used in conventional robotic technology are inadequate due to their large and varying inertias, friction and backlash. Mechanical devices with parallel actuation such as Stewart platforms (that employ parallel prismatic actuation and that are used for example in aircraft simulators) are some of the more promising fine-motion devices that essentially must trade off workspace for sensitivity of operation. Stewart platforms also have relatively complicated mechanical structure requiring many joints and have varying inertial parameters and usually a rather inhomogeneous force envelope, i.e. the resultant of leg forces is much higher in a particular direction than in others. If direct drive actuators are used in the legs of a Stewart platform, e.g. electric, hydraulic or pneumatic, each imparts different drawbacks and all result in a relatively expensive system.
Some of the most promising fine-motion technology employs electro dynamic or Lorentz magnetic levitation (maglev.). This technology provides six DOF frictionless motion with programmable compliance and has been used as a magnetically levitated robot wrist as well as a teleoperation master in a very highly sophisticated application for nano-telerobotic manipulation systems driving a scanning, tunnelling microscope in order to `feel atoms`. The device used incorporated a floater actuated by six flat coils operating in strong magnetic fields generated by NdFeB magnets attached to a stator. Controlled movement of the floater relative to the stator, programmable stiffness, as well as commanded forces and torques are achieved through optical sensing and digital feedback control of the coil current. These maglev devices are very suitable for fine-manipulation tasks but are limited to a very small range of motion; by their inability to provide high forces for long periods of time; and by their high cost.